Apparatus for encapsulating an integrated circuit package

Abstract

The present invention provides a method for fabricating an integrated circuit package, as well the resulting integrated circuit package, which retains a heatsink in close communication with a mold cavity. This precludes any encapsulant from flowing between the heatsink and the inner surface of a mold cavity. As a consequence, the bottom of the heatsink is not encapsulated and is thus exposed. This is accomplished by including posts, attached to the leadframe assembly, which have the function of exerting a downward force on a leadframe assembly and, in turn, on the heatsink. Tie bars, which are non-functional parts of a leadframe assembly, can be utilized as posts by bending the posts into an upright position.

I claim: 
     
       1. A apparatus for fabricating an integrated circuit package by encapsulating a semiconductor die connected to a leadframe and attached to a heatsink, comprising: an encapsulation mold having first and second portions, wherein an integrated circuit assembly comprising, a semiconductor die,   a leadframe, and   a heatsink having first and second surfaces, the first surface being on one side of the heatsink and the second surface being on the opposite side of the heatsink;   the leadframe and the semiconductor die being attached to the first surface of the heatsink, and the semiconductor die being connected to the leadframe;   wherein portions of the leadframe are bent away from the first surface of the heatsink a desired distance;     said integrated circuit assembly being placed in the first portion of said mold so that the second surface of the heatsink is in contact with a first inside surface of the first portion of said mold;   the second portion of said mold being placed over said integrated circuit assembly so that a second inside surface of the second portion of said mold is in contact with the bent portions of the leadframe, wherein the bent portions of the leadframe springingly bias the second surface of the heatsink toward the first inside surface of the first portion of said mold; and   encapsulant being injected into the first and second portions of said mold so as to encapsulate said integrated circuit assembly, wherein the bent portions of the leadframe keep the second surface of the heatsink in contact with the first inside surface of the first portion of said mold during injection of the encapsulant.   
     
     
       2. A apparatus for reducing the amount of undesired encapsulate that may form over a heatsink during fabrication of an integrated circuit package containing a semiconductor die attached to a leadframe and heatsink, comprising: a semiconductor die;   a leadframe having lead fingers, the semiconductor die connected to the leadfingers;   a heat sink attached to the leadframe;   portions of the leadframe being bent away from the heatsink a desired distance;   the semiconductor die, leadframe and heatsink being placed into a first portion of an encapsulation mold so that an outer surface of the heatsink is in contact with a first inside surface of the first portion of the mold;   a second portion of the encapsulation mold being placed over the semiconductor die, leadframe and heatsink so that a second inside surface of the second portion of the mold is in contact with the bent portions of the leadframe, wherein the bent portions of the leadframe springingly bias the outer surface of the heatsink toward the first inside surface of the first portion of the mold; and   encapsulant being injected into the first and second portions of the encapsulation mold so as to encapsulate the semiconductor die, leadframe and heatsink, wherein the bent portions of the leadframe keep the outer surface of the heatsink in contact with the first inside surface of the first portion of the mold so that the amount of undesired encapsulate flowing over the outer surface of the heatsink is reduced.   
     
     
       3. An integrated circuit package, comprising: a semiconductor die;   a heatsink;   a leadframe assembly comprising a plurality of leadframe fingers having proximate and distal ends, a portion of the leadframe assembly being disposed over a first surface of the heatsink, the semiconductor die being disposed in an opening of the leadframe assembly formed by the proximate ends of the leadframe fingers, the semiconductor die being connected to the proximate ends of the leadframe fingers, and the semiconductor die being in thermal communication with the first surface of the heatsink;   a plurality of posts formed from the leadframe assembly by bending portions of the leadframe assembly away from the first surface of the heatsink a desired distance;   an encapsulation package around the semiconductor die, the lead frame assembly and the heat sink except the portion of the distal ends of the leadframe fingers and a second surface of the heatsink, wherein the encapsulation package is formed by placing the semiconductor die, heatsink and leadframe assembly into a mold, the plurality of posts engaging a first inside surface of the mold and biasing the second surface of the heatsink toward a second inside surface of the mold to minimize the space between the second surface of the heatsink and the second inside surface of the mold so as to substantially prevent encapsulant from flowing over the second surface of the heatsink.   
     
     
       4. The integrated circuit package of claim 3, wherein the desired distance is greater than the distance between the first inside surface of the mold and the leadframe assembly so that the plurality of posts springingly bias the heatsink toward the second inside surface of the mold when in the mold. 
     
     
       5. The integrated circuit package of claim 3, wherein the plurality of posts are perpendicular to the leadframe assembly and extend away from the first surface of the heatsink. 
     
     
       6. The integrated circuit package of claim 3, wherein the plurality of posts are formed by bending the portions of the leadframes from 45 to 90 degrees from the first surface of the leadframe. 
     
     
       7. The integrated circuit package of claim 3, wherein the plurality of posts are formed by bending the portions of the leadframes from 10 to 90 degrees from the first surface of the leadframe.